The invention relates to improvements in mechanisms for transmitting torque between driving and driven parts, especially between the crankshaft of an internal engine and the input shaft of a change-speed transmission in a motor vehicle. More particularly, the invention relates to improvements in torque transmitting mechanisms of the type wherein a first flywheel is connected to the output member of the engine, a second flywheel is connected or connectable to the input member of the transmission, and the means for transmitting torque between the flywheels comprises several dampers. Torque transmitting mechanisms of such character are disclosed in numerous pending United States and foreign patent applications as well as in numerous United States and foreign patents of the assignee.
U.S. Pat. No. 4,274,524 to Nakane discloses a rotational torque transmitting mechanism wherein the means for transmitting torque between the flywheels comprises a damper and a torque limiting clutch. The damper comprises coil springs and a friction generating device which latter operates in parallel with the coil springs. The torque limiting clutch is a slip clutch having a constant slip torque considerably exceeding the nominal torque which is generated by the engine, i.e., the slip clutch responds only when the transmitted torque fluctuates within a wide range.
The purpose of the patented mechanism is to reduce the stresses upon the power train between the engine and the wheels as well as to enhance the comfort of the passengers and to reduce noise. It has been found that the patented mechanism cannot operate satisfactorily within the entire RPM range of the engine, and one of the reasons for such failure is believed to be that the slip clutch responds only to very pronounced fluctuations of torque which is transmitted by the engine, i.e., well above the nominal torque of the engine. Moreover, the slip clutch transmits a pronounced torque also when the engine is operated at a low RPM, namely when the transmitted torque is small, with the result that the slip clutch cannot compensate for and/or counteract smaller fluctuations of torque when the RPM of the engine is low.